Process for producing propylene oxide

ABSTRACT

A process for producing propylene oxide, which comprises the following steps:
         oxidation step: a step of obtaining cumene hydroperoxide by oxidizing cumene;   epoxidation step: a step of obtaining propylene oxide and cumyl alcohol by reacting cumene hydroperoxide obtained in the oxidation step with propylene; and   conversion step: a step of obtaining cumene by subjecting cumyl alcohol obtained in the epoxidation step to hydrogenation-containing reaction and recycling the cumene to the oxidation step,   wherein a concentration of 1,2-epoxy-2-phenylpropane contained in the reaction mixture after the oxidation step, is 1% by weight or less.

TECHNICAL FIELD

The present invention relates to a process for producing propyleneoxide.

BACKGROUND ART

A process in which propylene is converted into propylene oxide usingcumene hydroperoxide obtained from cumene as an oxygen carrier, cumylalcohol produced together with propylene oxide is subjected tohydrogenolysis to obtain cumene and this cumene is used repeatedly, isdisclosed in Czechoslovakia patent CS140743 and JP2001-270880 A. Thoughthese processes are composed of the oxidation step, epoxidation step andhydrogenolysis step, it is difficult to say that they are necessarilysufficient in industrial efficiency.

DISCLOSURE OF THE INVENTION

An object of the invention is to provide a process for efficientlyproducing propylene having excellent characteristics in which propyleneis converted into propylene oxide using cumene hydroperoxide obtainedfrom cumene as an oxygen carrier, the cumene can be used repeatedly, andfurther oxidation can be carried out efficiency thereby being able toefficiently produce propylene oxide.

Namely, the present invention relates to a process for producingpropylene oxide, which comprises the following steps:

oxidation step: a step of obtaining cumene hydroperoxide by oxidizingcumene;

epoxidation step: a step of obtaining propylene oxide and cumyl alcoholby reacting cumene hydroperoxide obtained in the oxidation step withpropylene in the presence of an epoxidation catalyst; and

conversion step: a step of converting cumyl alcohol obtained in theepoxidation step into cumene and recycling said cumene to the oxidationstep,

wherein a concentration of 1,2-epoxy-2-phenylpropane contained in areaction mixture after the oxidation step is 1% by weight or less.

BEST MODE FOR CARRYING OUT THE INVENTION

The oxidation step is a step for obtaining cumene hydroperoxide byoxidizing cumene. The oxidation of cumene is usually conducted byauto-oxidation using an oxygen-containing gas such as air oroxygen-concentrated air. This oxidation may be conducted without use ofan additive, and an additive such as an alkali may be used. The reactiontemperature is usually from 50 to 200° C., and the reaction pressure isusually between atmospheric pressure and 5 MPa. In the oxidation methodin which the additive is used, an alkali metal compound such as NaOH orKOH, an alkaline earth metal compound, or alkali metal carbonate such asNa₂CO₃ or NaHCO₃, ammonia, (NH₄)₂CO₃, an alkali metal ammonium carbonateor the like, is used as an alkali reagent.

The epoxidation step is a step for obtaining propylene oxide and cumylalcohol by reacting cumene hydroperoxide obtained in the oxidation stepwith propylene. The epoxidation step is preferably conducted in thepresence of an epoxidation catalyst, particularly a catalyst containingtitanium-containing silicon oxide from the viewpoint of obtaining theobject compound under high yield and high selectivity. As the catalyst,so-called Ti-silica catalysts containing Ti chemically bonded to siliconoxide, are preferable. For example, a catalyst prepared by supporting aTi compound on a silica carrier, a catalyst prepared by combining a Ticompound with silicon oxide by a co-precipitation method or sol gelmethod, zeolite compounds containing Ti, and the like, can be listed.Cumene hydroperoxide used as a raw material in the epoxidation step, maybe a dilute or dense purified material or non-purified material.

The epoxidation is conducted by contacting propylene and cumenehydroperoxide with the catalyst. The reaction is carried out in a liquidphase using a solvent. The solvent should be liquid under a temperatureand a pressure during the reaction, and substantially inert to reactantsand products. The solvent may be a substance present in a hydroperoxidesolution to be used. For example, when cumene hydroperoxide is a mixturewith cumene which is a raw material thereof, the cumene can be used as asubstitute of a solvent without particularly adding a solvent.

The epoxidation temperature is usually from 0 to 200° C., and preferablyfrom 25 to 200° C. The pressure may be a pressure sufficient to keep thereaction mixture in a liquid condition. In general, the pressure isadvantageously from 100 to 10,000 kPa.

The solid catalyst can be advantageously used in the form of a slurry orfixed bed. In the case of a large-scale industrial operation, a fixedbed is preferably used. In addition, the epoxidation can be conducted bya batch-wise method, a semi-continuous method or a continuous method.

When a liquid containing a raw material for reaction is passed through afixed bed, the catalyst is not contained at all or substantially in aliquid mixture drawn out from the reaction zone.

The conversion step is a step for obtaining cumene by subjecting cumylalcohol obtained in the epoxidation step to hydrogenation-containingreaction and recycling the cumene to the oxidation step. As a method forconverting cumyl alcohol into cumene, a method of first dehydratingcumyl alcohol to obtain α-methylstyrene and then hydrogenatingα-methylstyrene to convert into cumene (dehydration-hydrogenationmethod), and a method of subjecting cumyl alcohol to hydrogenolysis todirectly convert into cumene, can be illustrated.

A case in which the conversion step is composed of the dehydration stepand hydrogenation step, is explained below.

It is preferable to separate propylene oxide obtained by the epoxidationfrom cumyl alcohol before the dehydration step from the viewpoint ofobtaining high yield of propylene oxide.

As a separation method, distillation can be used.

A catalyst used in the dehydration includes acids such as sulfuric acid,phosphoric acid and p-toluene sulfonic acid and metal oxides such asactivated alumina, titania, zirconia, silica-alumina and zeolites, andactivated alumina is preferable from viewpoints of separation from thereaction mixture, catalyst life, selectivity, etc.

The dehydration is usually conducted by contacting cumyl alcohol withthe catalyst, but, in the present invention, hydrogen may be fedtogether with cumyl alcohol to the catalyst to conduct hydrogenationsubsequent to the dehydration. The reaction can be conducted in a liquidphase using a solvent. The solvent should be substantially inert toreactants and products. The solvent may be a substance present in acumyl alcohol solution to be used. For example, when cumyl alcohol is amixture with cumene as a product, it is possible to use cumene as asubstitute without adding a solvent in particular. The dehydrationtemperature is usually 50 to 450° C., preferably 150 to 300° C. Inusual, the pressure is advantageously 10 to 10,000 kPa. The dehydrationcan be advantageously conducted by using a catalyst in a slurry form orfixed-bed form.

The hydrogenation step is a step for converting into cumene by supplyingα-methylstyrene obtained by the dehydration to a hydrogenation catalystto hydrogenate a-methylstyrene and for recycling cumene to the oxidationstep as a raw material in the oxidation step.

Though the hydrogenation catalyst includes catalysts containing a metalof Group 10 or 11 of the Periodic Table, and specifically, nickel,palladium, platinum and copper, palladium or copper are preferable fromviewpoints of suppression of hydrogenation of the aromatic ring and highyield. As a copper catalyst, copper, Raney copper, copper/chromium,copper/zinc, copper/chromium/zinc, copper/silica, copper/alumina and thelike are listed. As a palladium catalyst, palladium/alumina,palladium/silica, palladium/carbon and the like are listed. Thesecatalysts can be used alone or in combination of two or more.

Though the hydrogenation is usually carried out by contactingα-methylstyrene and hydrogen with the catalyst, a part or the whole ofwater generated may be separated by oil-water separation or the like ormay be supplied together with α-methylstyrene to the hydrogenationcatalyst for carrying out the hydrogenation subsequent to thedehydration.

Though the amount of hydrogen required in the reaction may be equimolarto α-methylstyrene theoretically, an excess amount of hydrogen isrequired because other components which consume hydrogen are containedin the raw material.

As a molar ratio of hydrogen to α-methylstyrene, the range of 1 to 10 isusually applied because the reaction proceeds rapidly with increase of apartial pressure of hydrogen. The range is further preferably 1 to 5.The excess amount of hydrogen remained after the reaction can berecycled after separated from the reaction mixture. The hydrogenationcan be conducted in a liquid phase using a solvent or gas phase. Thesolvent must be substantially inert to the reactants and products. Thesolvent may be a substance existing in an α-methylstyrene solution to beused. For example, when α-methylstyrene is a mixture with cumene as aproduct, it is possible to use cumene as a substitute of the solventwithout adding a solvent in particular. The hydrogenation temperature isusually 0 to 500° C., preferably 30 to 400° C. In usual, the pressure isadvantageously 100 to 10,000 kPa.

As modes of the dehydration and hydrogenation, these reactions can beadvantageously conducted by a continuous method using a catalyst in theform of a fix-bed. The dehydration and hydrogenation may be conductedusing separate reactors or a single reactor. As a reactor used in thecontinuous method, there are an adiabatic reactor and an isothermalreactor, and the adiabatic reactor is preferable because the isothermalreactor requires an apparatus for removal of heat. In a case of a singleadiabatic reactor, the temperature lowers with progress of the reactionbecause the dehydration of cumyl alcohol is an endothermic reaction, andon the other hand, since the hydrogenation of α-methylstyrene is anexothermic reaction, the temperature rises with progress of thereaction. The outlet temperature becomes higher than the inlettemperature because the generated heat quantity is larger in total.

The reaction temperature and pressure are selected so that watercontained in an α-methylstyrene solution after the dehydration, is notcondensed. The reaction temperature is preferably 150 to 300° C., andthe reaction pressure is preferably 100 to 2000 kPa. When thetemperature is too low or the pressure is too high, water may becondensed at the outlet of the dehydration, leading to deterioration ofthe performance of the hydrogenation catalyst. Further, when thepressure is too high, it is also disadvantageous in the reactionequilibrium of dehydration. When the temperature is too high or thepressure is too low, it may become disadvantageous because the catalystlife is shortened by howling or the like caused by much generation ofthe gas phase part.

Though hydrogen can be supplied from any one of an inlet of adehydration reactor and an inlet of a hydrogenation reactor, it ispreferable to supply from the inlet of the dehydration reactor in viewof the activity of the dehydration catalyst. That is, vaporization ofwater produced through dehydration is promoted by bringing into constantexistence of hydrogen in the dehydration zone and the equilibriumdehydration conversion rises, therefore, high conversion can be attainedeffectively compared to absence of hydrogen. Though water generated inthe dehydration is passed through the hydrogenation catalyst, it ispossible to operate at low cost without particularly setting up anapparatus for water removal as described above, by operating at thelevel not condensing water. Further, unreacted hydrogen in the outlet ofthe reactor can be recycled after gas-liquid separation operation.

Furthermore, at the time of the gas-liquid separation operation, it ispossible to separate water generated in the dehydration from thereaction mixture. A part of the obtained reaction mixture (mainlycumene) can be recycled to the inlet of the reactor for use.

An amount of the dehydration catalyst used may be an amount enough toconvert cumyl alcohol, and the conversion of cumyl alcohol is preferably90% or more. An amount of the hydrogenation catalyst used may be anamount enough to convert α-methylstyrene, and the conversion ofα-methylstyrene is preferably 98% or more.

Considering from a viewpoint of cost, the dehydration and hydrogenationcatalysts are preferably packed in single fixed bed reactor but not inmulti stage reactors. Inside of the reactor may be partitioned intoseveral beds or not. When the reactor is not partitioned, thedehydration catalyst and hydrogenation catalyst may be directlycontacted each other or those may be partitioned with an inert packing.

A case of which production of cumene from cumyl alcohol is conducted byhydrogenolysis, is explained below:

The hydrogenolysis step is a step for obtaining cumene by subjectingcumyl alcohol obtained in the epoxidation step to hydrogenolysis and forrecycling the cumene as a raw material to the oxidation step. In otherwords, cumene which has been used in the oxidation step is reproduced bythe hydrogenolysis. The hydrogenolysis is carried out by contactingcumyl alcohol and hydrogen with a catalyst. As the catalyst, anycatalyst having hydrogenation ability can be used. Though examples ofthe catalyst include metal-based catalysts of metals of Groups 8 to 10such as cobalt, nickel and palladium metal and metal-based catalysts ofmetals of Groups 11 and 12 such as copper and zinc, copper-basedcatalysts are preferable from the viewpoint of suppression ofby-products.

As the copper-based catalyst, copper, Raney copper, copper-chromium,copper-zinc, copper-chromium-zinc, copper-silica, copper-alumina and thelike are listed.

The reaction can be conducted in a liquid phase using a solvent or a gasphase. The solvent should be substantially inert to the reactants andproducts. The solvent may be a substance existing in a cumyl alcoholsolution to be used. For example, when cumyl alcohol is a mixture withcumene as a product, it is possible to use cumene as a substitute of thesolvent without adding a solvent in particular.

Though the amount of hydrogen required in the hydrolysis may beequimolar to cumyl alcohol, an excess amount of hydrogen is requiredbecause other components which consume hydrogen, are contained in theraw material. Further, the molar ratio of hydrogen to cumyl alcohol isusually from 1 to 10 because the reaction proceeds rapidly with increaseof a partial pressure of hydrogen. The ratio is further preferably from1 to 5. The excess amount of hydrogen remained after the reaction may berecycled after separated from the reaction mixture. The hydrogenolysistemperature is usually 0 to 500° C., preferably 30 to 400° C. In usual,the pressure is advantageously 100 to 10,000 kPa. The hydrolysis can beadvantageously carried out using a catalyst in the form of slurry or afixed bed.

The present process can be conducted by a batch method, semi-continuousmethod or continuous method.

When a liquid or gas containing a raw material for reaction is passedthrough a fixed bed, the catalyst is not contained at all orsubstantially in a liquid mixture drawn out from the reaction zone.

In the present invention, it is required that a concentration of1,2-epoxy-2-phenylpropane contained in the reaction mixture after theoxidation step is 1% by weight or less, and 0.5% by weight or less ispreferred.

When the concentration of 1,2-epoxy-2-phenylpropane contained in thereaction mixture after the oxidation step is over 1% by weight, areaction yield in the oxidation step deteriorates because amounts ofcumyl alcohol and acetophenone formed increase. Though cumyl alcohol canbe returned to cumene via the hydrogenation step, it is not preferredeconomically as a process of propylene oxide production because hydrogenof equimolar to cumyl alcohol, is consumed. In addition, acetophenone isa compound in which the carbon number was reduced, therefore, itconverts into ethylbenzene via the conversion step, leading to a loss ofcumene.

Though distillation removal, removal through reaction, adsorptionremoval and the like are listed as methods for controlling the1,2-epoxy-2-phenylpropane concentration to the range within the presentinvention, it is preferable as a method of controlling generation of1,2-epoxy-2-phenylpropane to optimize the reaction conditions ofoxidation such as temperature and time or to reduce alcohols and olefinsother than cumene as much as possible.

EXAMPLE Example 1

Cumene recycled from a hydrogenation step was mixed with an aqueoussolution of 1.5 wt.% of sodium carbonate in a weight ratio of 1 of theaqueous solution to 20 of cumene, and the mixture was reacted under apressure of 630 kPa and a temperature of 90 to 105° C. for 5 hourssupplying air.

At this time, a concentration of 1,2-epoxy-2-phenylpropane was 0.2% byweight. A formed oxidized liquid had the following composition.

Cumene hydroperoxide 14.6% by weight Cumyl alcohol  0.1% by weightCumene 83.9% by weight Acetophenone  0.1% by weight

Example 2

A reaction operation was carried out in the same manner as in Example 1except that the amount of cumene recycled from the hydrogenation step,was changed.

At this time, a concentration of 1,2-epoxy-2-phenylpropane was 0.6% byweight. A formed oxidized liquid had the following composition.

Cumene hydroperoxide 24.4% by weight Cumyl alcohol  1.3% by weightCumene 72.6% by weight Acetophenone  0.4% by weight

Comparative Example 1

A reaction operation was carried out in the same manner as in Example 1except that the amount of cumene recycled from the hydrogenation step,was changed.

At this time, a concentration of 1,2-epoxy-2-phenylpropane was 1.5% byweight. A formed oxidized liquid had the following composition.

Cumene hydroperoxide 25.4% by weight Cumyl alcohol  2.0% by weightCumene 68.8% by weight Acetophenone  0.7% by weight

INDUSTRIAL APPLICABILITY

According to the present invention, there could be provided a processfor producing propylene oxide, which can convert propylene intopropylene oxide using cumene hydroperoxide obtained from cumene as anoxygen carrier, use repeatedly the cumene and further efficiently carryout oxidation thereby being able to efficiently produce propylene oxide.

1. A process for producing propylene oxide, which comprises thefollowing steps: oxidation step: a step of obtaining cumenehydroperoxide by oxidizing cumene; epoxidation step: a step of obtainingpropylene oxide and cumyl alcohol by reacting cumene hydroperoxideobtained in the oxidation step with propylene; and conversion step: astep of obtaining cumene by subjecting cumyl alcohol obtained in theepoxidation step to hydrogenation-containing reaction and recycling thecumene to the oxidation step, wherein a concentration of1,2-epoxy-2-phenylpropane contained in a reaction mixture after theoxidation step is 1% by weight or less.
 2. The process according toclaim 1, wherein the conversion step comprises the following steps:dehydration step: a step of obtaining α-methylstyrene by dehydratingcumyl alcohol obtained in the epoxidation step in the presence of adehydration catalyst; and hydrogenation step: a step of obtaining cumeneby hydrogenating α-methylstyrene in the presence of a hydrogenationcatalyst to obtain cumene, and recycling the cumene to the oxidationstep.
 3. The process according to claim 1, wherein the conversion stepcomprises the following step: hydrogenolysis step; a step of obtainingcumene by subjecting cumyl alcohol obtained in the epoxidation step tohydrogenolysis in the presence of a hydrogenolysis catalyst, andrecycling the cumene to the oxidation step as the raw material.